Method and control device for operating an internal combustion engine

ABSTRACT

A method is provided for operating an internal combustion engine ( 10 ) that has at least one cylinder row ( 11   a,    11   b ) with multiple cylinders ( 12   a,    12   b ). Each cylinder row ( 11   a,    11   b ) has a first exhaust-gas turbocharger ( 13   a,    13   b ) and a second exhaust-gas turbocharger ( 14   a,    14   b ). The method includes providing charge air for the cylinders ( 12   a,    12   b ) of the internal combustion engine ( 10 ) either exclusively by the first exhaust-gas turbocharger ( 13   a,    13   b ) of the cylinder row ( 11   a   , 11   b ) of the internal combustion engine ( 10 ) or by both the first exhaust-gas turbocharger ( 13   a,    13   b ) of the cylinder row ( 11   a   , 11   b ) of the internal combustion engine ( 10 ) and the second exhaust-gas turbocharger ( 14   a,    14   b ) of the cylinder row ( 11   a   , 11   b ) of the internal combustion engine ( 10 ) in a manner dependent on an operating mode demanded by a driver and/or by a controller for the internal combustion engine ( 10 ).

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 to German Patent Appl. No. 10 2014 116 639.6 filed on Nov. 13, 2014, the entire disclosure of which is incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The invention relates to a method for operating an internal combustion engine and to a control device for carrying out the method.

2. Description of the Related Art

DE 10 2007 046 655 A1 discloses an internal combustion engine that has a cylinder row of multiple cylinders. Each cylinder of the cylinder row has multiple outlet valves for exhaust gas. More particularly, a first exhaust-gas duct couples first outlet valves of the cylinders of the cylinder row to a first turbine of a first exhaust-gas turbocharger, and a second outlet duct couples second outlet valves to a turbine of a second exhaust-gas turbocharger. A first charge-air line couples a compressor of the first exhaust-gas turbocharger to the cylinders of the cylinder row, and a second charge-air line couples a compressor of the second exhaust-gas turbocharger to the cylinders of the cylinder row. Exhaust gas exiting the cylinders of the internal combustion engine is conducted either exclusively via the first exhaust-gas turbocharger or alternatively via both the first and second exhaust-gas turbochargers. The two exhaust-gas turbochargers are connected in parallel with one another. When the exhaust gas is conducted exclusively via the turbine of the first exhaust-gas turbocharger, the exhaust gas exits the cylinders exclusively via the first outlet valves of said cylinders. By contrast, when the exhaust gas is conducted in parallel via the turbines of both exhaust-gas turbochargers, the exhaust gas can exit the cylinders of the cylinder row via both outlet valves in parallel. Such an internal combustion engine also is referred to as an internal combustion engine with sequential supercharging.

Internal combustion engines with sequential supercharging are known from DE 10 2007 046 655 A1, DE 10 2007 046 656 A1 and DE 10 2008 036 308 B4. However, there is a demand for improving the operation of such an internal combustion engine to utilize the sequential supercharging optimally.

It is an object of the invention to provide a novel method for operating an internal combustion engine, and a control device for carrying out the method.

SUMMARY

According to the invention, charge air for the cylinders of the internal combustion engine is provided either exclusively by the first exhaust-gas turbocharger of the or of each cylinder row of the internal combustion engine or both by the first and second exhaust-gas turbochargers of the or of each cylinder row of the internal combustion engine in a manner dependent on an operating mode demanded by a driver and/or by a controller for the internal combustion engine. Thus, the decision how charge air is provided via the exhaust-gas turbochargers is made in a manner dependent on an operating mode demanded by a driver and/or by a controller.

The exhaust gas may be conducted virtually exclusively via the first exhaust-gas turbocharger when charge air is provided exclusively by the first exhaust-gas turbocharger of a cylinder row of the internal combustion engine. In this case, a small exhaust-gas flow rate may be conducted via the second exhaust-gas turbocharger to keep the second exhaust-gas turbocharger running. However, the second exhaust-gas turbocharger does not provide charge air for the cylinders of the internal combustion engine. Alternatively, the entire exhaust-gas flow rate may be conducted via the first exhaust-gas turbocharger.

When charge air for the cylinders of the internal combustion engine is provided by both the first and second exhaust-gas turbochargers of a cylinder row, the exhaust gas is conducted partially via each of the first and second exhaust-gas turbochargers so that both exhaust-gas turbochargers participate in the provision of the charge air.

Charge air for the cylinders of the internal combustion engine may be provided either exclusively by the first exhaust-gas turbocharger of a cylinder row of the internal combustion engine or both by the first and second exhaust-gas turbochargers of the cylinder row of the internal combustion engine in a manner dependent on the operating mode demanded by a driver and/or by a controller for the internal combustion engine, and specifically in a manner dependent on the torque provided by the internal combustion engine and/or on the speed of the internal combustion engine. This torque-dependent and/or engine speed-dependent provision of charge air by the exhaust-gas turbochargers of the internal combustion engine may be utilized in an economy operating mode of the internal combustion engine. The economy operating mode provides charge air for the cylinders of the internal combustion engine exclusively by the first exhaust-gas turbocharger of a cylinder row of the internal combustion engine when the torque provided by the internal combustion engine is relatively high but speeds of the internal combustion engine are relatively low. Conversely, charge air for the cylinders of the internal combustion engine is provided both by the first and second exhaust-gas turbochargers of the cylinder row of the internal combustion engine at relatively high speeds and high torque of the internal combustion engine.

Charge air for the cylinders of the internal combustion engine may be provided both by the first and second exhaust-gas turbochargers of a cylinder row in the economy operating mode of the internal combustion engine, when the torque provided by the internal combustion engine is relatively low regardless of the speed of the internal combustion engine. In this way, the sequential supercharging can be utilized advantageously in an economy operating mode demanded by a controller or by a driver, thereby achieving low fuel consumption. The economy operating mode may be demanded by a driver by actuation of a corresponding button or switch.

Charge air for the cylinders of the internal combustion engine may be provided either exclusively by the first exhaust-gas turbocharger of a cylinder row of the internal combustion engine or both by the first and second exhaust-gas turbochargers of the cylinder row in a manner dependent on the operating mode demanded by a driver and/or by a controller and in a manner dependent on the power of the internal combustion engine. This power-dependent provision of charge air may be utilized in a sport operating mode of the internal combustion engine, which is an operating mode of the internal combustion engine configured for driving operation with high driving dynamics. Specifically, charge air for the cylinders of the internal combustion engine is provided by both the first and second exhaust-gas turbochargers of a cylinder row of the internal combustion engine in the sport operating mode of the internal combustion engine when relatively high power of the internal combustion engine is demanded by a driver.

Charge air for the cylinders of the internal combustion engine is provided exclusively by the first exhaust-gas turbocharger of a cylinder row of the internal combustion engine in the sport operating mode of the internal combustion engine when relatively low power of the internal combustion engine is demanded by a driver. In this way, the sequential supercharging can be utilized advantageously in a sport operating mode demanded by a controller or by a driver of the internal combustion engine. The sport operating mode of the internal combustion engine may be demanded by a driver by actuation of a corresponding button or switch.

Charge air for the cylinders of the internal combustion engine may be provided exclusively by the first exhaust-gas turbocharger of a cylinder row of the internal combustion engine when a catalytic converter heating operating mode is demanded upon a cold start of the internal combustion engine. In this way, the sequential supercharging can be utilized advantageously for heating a catalytic converter of the internal combustion engine after a cold start of the internal combustion engine.

Exemplary embodiments of the invention will be discussed in more detail on the basis of the drawing, without the invention being restricted to these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematized illustration of an internal combustion engine.

FIG. 2 is a first diagram for illustrating the method of the invention.

FIG. 3 is a second diagram for illustrating the method of the invention.

FIG. 4 is a third diagram for illustrating the method of the invention.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates an internal combustion engine 10 that can be operated in accordance with the method of the invention and/or the control device of the invention. The internal combustion engine 10 of FIG. 1 comprises two cylinder rows 11 a, 11 b with multiple cylinders 12 a, 12 b in each row. Each cylinder row 11 a, 11 b is assigned two exhaust-gas turbochargers 13 a, 14 a and 13 b, 14 b respectively.

First exhaust-gas turbochargers 13 a, 13 b of each cylinder row 11 a, 11 b are coupled to the cylinders 12 a, 12 b of the respective cylinder row 11 a, 11 b so that the exhaust gas of the respective cylinders 12 a, 12 b can be supplied to a turbine 15 a, 15 b of the respective first exhaust-gas turbocharger 13 a, 13 b proceeding from first outlet valves 16 a, 16 b of the cylinders 12 a, 12 b. The first outlet valves 16 a, 16 b of the cylinders 12 a, 12 b of the respective cylinder row 11 a, 11 b are coupled via a first exhaust line 17 a, 17 b to the respective turbine 15 a, 15 b of the respective first exhaust-gas turbocharger 13 a, 13 b.

Energy obtained in the turbines 15 a, 15 b of the first exhaust-gas turbochargers 13 a, 13 b is utilized in compressors 18 a, 18 b of the respective first exhaust-gas turbochargers 13 a, 13 b to compress charge air in the compressors. The charge air can be supplied from the compressors 18 a, 18 b of the first exhaust-gas turbochargers 13 a, 13 b to the cylinders 12 a, 12 b of the internal combustion engine 10 via first charge-air lines 19 a, 19 b.

The two exhaust-gas turbochargers 13 a, 14 a and 13 b, 14 b associated with each respective cylinder row 11 a, 11 b are connected in parallel. The exhaust gas of the cylinders 12 a, 12 b of the respective cylinder row 11 a, 11 b can be supplied to a turbine 20 a, 20 b of the respective second exhaust-gas turbocharger 14 a, 14 b of the respective cylinder row 11 a, 11 b proceeding from second outlet valves 21 a, 21 b of the cylinders 12 a, 12 b via a second exhaust line 22 a, 22 b. Energy obtained in the turbines 20 a, 20 b of the second exhaust-gas turbochargers 14 a, 14 b is utilized in compressors 23 a, 23 b of the second exhaust-gas turbochargers 14 a, 14 b to compress charge air. The charge air can be supplied from the compressors 23 a, 23 b of the second exhaust-gas turbochargers 14 a, 14 b to the cylinders 12 a, 12 b via a second charge-air line 24 a, 24 b.

In the exemplary embodiment of the internal combustion engine 10 shown in FIG. 1, each cylinder row 11 a, 11 b is assigned a charge-air cooler 25 a, 25 b. The charge-air lines 19 a, 24 a of the exhaust-gas turbochargers 13 a, 14 a of the cylinder row 11 a issue into the charge-air cooler 25 a, and the charge-air lines 19 b, 24 b of the exhaust-gas turbochargers 13 b, 14 b of the cylinder row 11 b issue into the charge-air cooler 25 b. Cooled charge air can be supplied from the charge-air coolers 25 a, 25 b, via charge-air lines 26 a, 26 b, 27 to the cylinders 12 a, 12 b of the cylinder rows 11 a, 11 b. Compressed charge air passes into the cylinders 12 a, 12 b via inlet valves 28 a, 28 b thereof.

The charge-air lines 26 a, 26 b merge into the charge-air line 27 downstream of the charge-air coolers 25 a, 25 b, and a throttle flap 30 is in the charge-air line 27 downstream of a merging point 29 of the charge-air lines 26 a, 26 b as viewed in the flow direction of the charge air.

Each turbine 15 a, 15 b, 18 a, 18 b of each of the exhaust-gas turbochargers 13 a, 14 a, 13 b, 14 b has a wastegate valve 31 a, 31 b, 32 a, 32 b. The wastegate valve 31 a assigned to the turbine 15 a of the first exhaust-gas turbocharger 13 a of the cylinder row 11 a enables exhaust gas to be conducted past the turbine 15 a of the first exhaust-gas turbocharger 13 a of the cylinder row 11 a so that the exhaust gas does not flow through the respective turbine 15 a, but is supplied, downstream of said turbine 15 a directly to a catalytic converter 33 a of the respective cylinder row 11 a for exhaust-gas purification purposes. The wastegate valve 32 a assigned to the turbine 20 a of the second exhaust-gas turbocharger 14 a of the cylinder row 11 a enables exhaust gas to be conducted past the turbine 20 a of the second exhaust-gas turbocharger 14 a and supplied directly to the catalytic converter 33 a. Similarly, the wastegate valves 31 b, 32 b of the turbines 15 b, 20 b of the two exhaust-gas turbochargers 13 b, 14 b of the cylinder row 11 b enable exhaust gas exiting the cylinders 12 b of the cylinder row 11 b to be conducted past the respective turbine 15 b, 20 b and discharged directly into a catalytic converter 33 b assigned to the cylinder row 11 b.

The charge-air side of each of the first exhaust-gas turbochargers 13 a, 13 b has an overrun air recirculation valve 34 a, 34 b. Compressed charge air can be discharged from the respective first charge-air line 19 a, 19 b via the respective overrun air recirculation valve 34 a, 34 b when the respective overrun air recirculation valve 34 a, 34 b. Thus, the compressed charge air is not supplied to the respective charge-air cooler 25 a, 25 b, but rather is discharged into the surroundings, for example into an air filter (not shown) assigned to the respective exhaust-gas turbocharger 13 a, 13 b.

Similarly, the charge air side of each of the second exhaust-gas turbochargers 14 a, 14 b has an air recirculation valve 35 a, 35 b and a compressor activation valve 36 a, 36 b. The flow cross section of the air recirculation valves 35 a, 35 b may differ from the flow cross section of the overrun air recirculation valves 34 a, 34 b.

Charge air compressed in the compressors 23 a, 23 b of the second exhaust-gas turbochargers can be discharged from the respective second charge-air line 24 a, 24 b into the surroundings via an air filter of the respective exhaust-gas turbocharger when the air recirculation valves 35 a, 35 b of the second exhaust-gas turbochargers 14 a, 14 b are open so that the corresponding charge air is not supplied to the respective charge-air cooler 25 a, 25 b.

The second charge-air lines 24 a, 24 b are separated in terms of flow from the respective charge-air cooler 25 a, 25 b when the compressor activation valves 36 a, 36 b are closed. However, the open compressor activation valves 36 a, 36 b permit a flow through the second charge-air lines 24 a, 24 b in the direction of the charge-air coolers 25 a, 25 b.

Arrows 37 in FIG. 1 denote an exhaust-gas flow, and arrows 38 denote a charge-air flow.

A control device 39 controls the internal combustion engine 10. More particularly, the control device 39 generates control signals for the control, specifically for the control of the outlet valves 16 a, 16 b, 21 a, 21 b and for the control of the inlet valves 28 a, 28 b of the cylinders 12 a, 12 b, as indicated by the dashed lines in FIG. 1. Furthermore, the control device 39 generates control signals for the control of: the wastegate valves 31 a, 31 b, 32 a, 32 b, the overrun air recirculation valves 34 a, 34 b, the air recirculation valves 35 a, 35 b, and the compressor activation valves 36 a, 36 b. Alternatively, the compressor activation valves 36 a, 36 b may be passive, spring-loaded valves. The control device 39 also generates a control signal for the throttle flap 30.

Each catalytic converter 33 a, 33 b has a temperature sensor 40 a, 40 b that provides an actual temperature value of the respective catalytic converter 33 a, 33 b to the control device 39. A virtual software temperature sensor may be utilized instead of a hardware temperature sensor 40 a, 40 b to calculate the actual temperature value of the respective catalytic converter 33 a, 33 b on the basis of a model.

The exhaust gas produced in the cylinders 12 a, 12 b of the respective cylinder row 11 a, 11 b can be conducted virtually exclusively via the respective first exhaust-gas turbocharger 13 a, 13 b or alternatively partially via the first exhaust-gas turbocharger 13 a, 13 b and partially via the second exhaust-gas turbocharger 14 a, 14 b of the respective cylinder row 11 a, 11 b.

When the exhaust gas is conducted virtually exclusively via the first exhaust-gas turbocharger 13 a, 13 b of the respective cylinder row 11 a, 11 b, the first outlet valves 16 a, 16 b are operated with a relatively large valve lift, hereinafter referred to as maximum lift, and the second outlet valves 21 a, 21 b are operated with a relatively small valve lift, hereinafter referred to as minimum lift. Thus, the exhaust gas is supplied virtually entirely to the turbine 15 a, 15 b of the respective first exhaust-gas turbocharger 13 a, 13 b, and only a small exhaust-gas flow rate passes into the region of the turbines 20 a, 20 b of the second exhaust-gas turbochargers 14 a, 14 b. In this condition, the air recirculation valve 35 a, 35 b is open and the compressor activation valve 36 a, 36 b is closed. Thus, this part of the charge-air flow is not delivered to the cylinders 12 a, 12 b, but rather is discharged into the surroundings. Charge air for the cylinders then is provided exclusively by the first exhaust-gas turbochargers 13 a, 13 b. The overrun air recirculation valve 34 a, 34 b assigned to the respective compressor 18 a, 18 b of the respective first exhaust-gas turbocharger 13 a, 13 b is closed in this case.

Alternatively, when charge air is provided exclusively by the first exhaust-gas turbocharger of a cylinder row, the entire exhaust-gas flow rate may be conducted via the first exhaust-gas turbocharger. In this case, the minimum lift is a zero lift.

Charge air for the cylinders 12 a, 12 b is provided by both exhaust-gas turbochargers 13 a, 14 b when the exhaust gas of the cylinders 12 a, 12 b of the respective cylinder row 11 a, 11 b is conducted partially via the first exhaust-gas turbocharger 13 a, 13 b and partially via the second exhaust-gas turbocharger 14 a, 14 b. In this condition, both the first outlet valves 16 a, 16 b and the second outlet valves 21 a, 21 b are operated with maximum lift to supply exhaust gas to the turbines 15 a, 20 a, 15 b, 20 b of both exhaust-gas turbochargers 13 a, 14 a, 13 b, 14 b. Thus, charge air is compressed in the exhaust-gas turbochargers and is supplied to the cylinders 12 a, 12 b. In this case, both the overrun air recirculation valves 34 a, 34 b and the air recirculation valves 35 a, 35 b are closed, while the compressor activation valves 36 a, 36 b are open.

As stated above, the exhaust gas produced in the cylinders 12 a, 12 b of the cylinder rows 11 a, 11 b may be utilized for supercharging of charge air. The charge air for the cylinders 12 a, 12 b of the internal combustion engine 10 is provided either exclusively by the first exhaust-gas turbocharger 13 a, 13 b of the cylinder rows 11 a, 11 b or by both the first exhaust-gas turbocharger 13 a, 13 b of the cylinder rows 11 a, 11 b and the second exhaust-gas turbocharger 14 a, 14 b of the cylinder rows 11 a, 11 b. The decision as to whether the charge-air supercharging is performed exclusively by the first exhaust-gas turbochargers 13 a, 13 b or by the first and second exhaust-gas turbochargers 13 a, 13 b, 14 a, 14 b is made in a manner dependent on an operating mode demanded by a driver and/or by a controller of the internal combustion engine. In particular, a driver may demand an economy operating mode or a sport operating mode, while the controller of the internal combustion engine may demand a catalytic converter heating operating mode.

In a first embodiment of the method, charge air for the cylinders 12 a, 12 b of the internal combustion engine 10 is provided either exclusively by the first exhaust-gas turbocharger 13 a, 13 b of the two cylinder rows 11 a, 11 b or both by the first exhaust-gas turbocharger 13 a, 13 b and by the second exhaust-gas turbocharger 14 a, 14 b of the cylinder rows 11 a, 11 b in a manner dependent on the operating mode demanded by a driver and/or by a controller for the internal combustion engine, and also in a manner dependent on the demanded power of the internal combustion engine. This power-dependent and operating mode-dependent charge-air supercharging is preferably performed when a sport operating mode for the internal combustion engine is demanded by a driver by actuation of a switch or by actuation of a button.

FIG. 2 shows a diagram in which a torque M is plotted versus the speed n of the internal combustion engine. The solid line in FIG. 2 corresponds to a full-load characteristic curve 41 of the internal combustion engine. The product of torque M and speed n corresponds to the power of the internal combustion engine. The dashed line in FIG. 2 shows a characteristic map boundary 42 between charge-air supercharging exclusively by the first exhaust-gas turbochargers 13 a, 13 b of the cylinder rows 11 a, 11 b and charge-air supercharging by both by the first exhaust-gas turbochargers 13 a, 13 b and the second exhaust-gas turbochargers 14 a, 14 b of the cylinder rows 11 a, 11 b. A switch is made automatically upon overshooting the characteristic map boundary 42.

The operation of providing the charge air exclusively by the respective first exhaust-gas turbochargers 13 a, 13 b is referred to as a single-charger operation of the respective cylinder row 11 a, 11 b. The operation of providing charge air by both exhaust-gas turbochargers 13 a, 14 a and 13 b, 14 b is referred to as a two-charger operation of the respective cylinder row 11 a, 11 b.

The charge air for the cylinders 12 a, 12 b of the internal combustion engine 10 is provided exclusively by the first exhaust-gas turbochargers 13 a, 13 b of the cylinder rows 11 a, 11 b when a sport operating mode for the internal combustion engine 10 is demanded, and when the power demanded of the internal combustion engine is relatively low. By contrast, the charge air for the cylinders 12 a, 12 b of the internal combustion engine 10 is provided both by the first exhaust-gas turbochargers 13 a, 13 b and by the second exhaust-gas turbochargers 14 a, 14 b in the sport operating mode, when the power demanded of the internal combustion engine is relatively high.

The region 43 in the engine speed-torque characteristic map of FIG. 2 denotes the sport operating mode of the internal combustion engine 10 where the charge-air supercharging is performed exclusively by the first exhaust-gas turbochargers 13 a, 13 b. The region 44 of the engine speed-torque characteristic map of FIG. 2 denotes the sport operating mode of the internal combustion engine 10 where the charge-air supercharging is performed by both the first exhaust-gas turbochargers 13 a, 13 b and the second exhaust-gas turbochargers 14 a, 14 b.

FIG. 3 illustrates the engine speed-torque characteristic curve when an economy operating mode for the internal combustion engine 10 is demanded by a driver by actuation of a switch or a button. The engine speed-torque characteristic curve of FIG. 3 shows the full-load characteristic curve 41 and a characteristic map boundary 45 that separates a region 46 in which the charge-air supercharging is performed exclusively by the first exhaust-gas turbochargers 13 a, 13 b from a region 47 in which the charge-air supercharging is performed by both the first exhaust-gas turbochargers 13 a, 13 b and the second exhaust-gas turbochargers 14 a, 14 b.

Region 46 of the characteristic map of FIG. 3 identifies conditions where charge air for the cylinders 12 a, 12 b of the internal combustion engine 10 is provided exclusively by the first exhaust-gas turbochargers 13 a, 13 b of the two cylinder rows 11 a, 11 b of the internal combustion engine 10 when an economy operating mode for the internal combustion engine 10 is demanded and when the torque M provided by the internal combustion engine is relatively high at relatively low speeds n of the internal combustion engine in the characteristic map region 46. On the other hand, region 47 of the characteristic map of FIG. 3 identifies conditions where the charge air for the cylinders 12 a, 12 b is provided by both the first exhaust-gas turbochargers 13 a, 13 b and the second exhaust-gas turbochargers 14 a, 14 b of the two cylinder rows 11 a, 11 b in the case of relatively high torques M and relatively high speeds n of the internal combustion engine 10 in the economy operating mode.

In the economy operating mode, when the torque M provided by the internal combustion engine is relatively low, the charge air for the cylinders 12 a, 12 b is provided both by the first exhaust-gas turbochargers 13 a, 13 b and by the second exhaust-gas turbochargers 14 a, 14 b of the cylinder rows 11 a, 11 b regardless of the speed n of the internal combustion engine 10 in the characteristic map region 47. Accordingly, in the economy operating mode, the charge-air supercharging is performed independently of the torque M and independently of the speed n of the internal combustion engine 10.

As stated above, the economy operating mode is designed for fuel-saving operation of the internal combustion engine 10. On the other hand, the sport operating mode is designed for operation with high driving dynamics. The driver can demand the economy operating mode or the sport driving mode by actuating a switch or a button.

A catalytic converter heating operating mode is demanded by a controller in the event of a cold start of the internal combustion engine 10 or as a result of a catalytic converter temperature being identified as being too low by a hardware or virtual temperature sensor 40 a, 40 b. Charge air for the cylinders 12 a, 12 b of the internal combustion engine 10 is provided exclusively by the first exhaust-gas turbocharger 13 a, 13 b of the cylinder rows 11 a, 11 b in the catalytic converter heating operating mode.

According to the invention, supercharging of the charge air can be performed independently of an operating mode demanded by a driver and/or by a controller, of the internal combustion engine 10, wherein the charge air is provided either by both exhaust-gas turbochargers 13 a, 14 a and 13 b, 14 b, of each cylinder row 11 a, 11 b or exclusively by a single exhaust-gas turbocharger 13 a, 13 b of each cylinder row 11 a, 11 b.

Single-charger operation is implemented at the respective cylinder row 11 a, 11 b when charge air for the cylinders 12 a, 12 b of the internal combustion engine 10 is provided exclusively by the first exhaust-gas turbochargers 13 a, 13 b of the respective cylinder row 11 a, 11 b. The first outlet valves 16 a, 16 b are operated with a relatively large valve lift or with maximum lift and the second outlet valves 21 a, 21 b are operated with a relatively small valve lift or with minimum lift or alternatively with zero lift when the single-charger operation is implemented at the respective cylinder row 11 a, 11 b. During this single-charger operation of the respective cylinder row 11 a, 11 b, in a steady-state operating state, the respective overrun air recirculation valve 34 a, 34 b is closed, the respective air recirculation valve 35 a, 35 b is open, and the respective compressor activation valve 36 a, 36 b is closed.

The respective cylinder row 11 a, 11 b is operated in two-charger operation when charge air for the cylinders 12 a, 12 b of the internal combustion engine is provided by both exhaust-gas turbochargers 13 a, 13 b, 14 a, 14 b of the cylinder rows 11 a, 11 b. During such two-charger operation, both outlet valves 16 a, 16 b, 21 a, 21 b of each cylinder 12 a, 12 b are operated with relatively large valve lift or with maximum lift. In the case of two-charger operation of the respective cylinder row 11 a, 11 b, in a steady-state operating mode, the respective overrun air recirculation valve 34 a, 34 b is closed, the respective air recirculation valve 35 a, 35 b is closed, and the respective compressor activation valve 36 a, 36 b is open.

Defined measures are implemented to switch optimally from single-charger operation of the respective cylinder row 11 a, 11 b to two-charger operation thereof above the induction-based full load of the internal combustion engine 10, while avoiding turbo lag. The defined measures are implemented first in preparation for the switch and second to perform the actual switch from single-charger operation to two-charger operation of the respective cylinder row 11 a, 11 b. When the internal combustion engine is operated above the induction-based full load, and when a speed of the internal combustion engine 10 reaches or overshoots a threshold value, a charge pressure or an intake pipe pressure is increased in preparation for the switch from single-charger operation to two-charger operation of the respective cylinder row 11 a, 11 b to maintain a driver demand torque and to build up a torque reserve and a charge pressure reserve. When the charge pressure reaches or overshoots a threshold value, a switch is made from single-charger operation to two-charger operation of the respective cylinder row 11 a, 11 b, and subsequently, the torque reserve and the charge-pressure reserve are eliminated again. The charge-pressure reserve is dependent on the pressure upstream of the throttle flap or on the pressure in the intake pipe.

Further details regarding the switch from single-charger operation to two-charger operation of the respective cylinder row 11 a, 11 b in the event of operation of the internal combustion engine 10 above the induction-based full load are described below with reference to FIG. 4 where multiple curve profiles with respect to time are plotted versus the time t.

A curve profile 48 visualizes a profile with respect to time of the speed of the internal combustion engine 10. A curve profile 49 visualizes the present charger operation of the respective cylinder row 11 a, 11 b, where the state “0” corresponds to single-charger operation, and the state “1” corresponds to two-charger operation of the respective cylinder row 11 a, 11 b. Curve profiles 50 and 51 visualize the state of the wastegate valves 31 a, 31 b and 32 a, 32 b. More particularly, the curve profile 50 visualizes the state of the wastegate valves 31 a, 31 b that interact with the respective first exhaust-gas turbocharger 13 a, 13 b of the respective cylinder row 11 a, 11 b, whereas the curve profile 51 visualizes the state of the wastegate valves 32 a, 32 b that interact with the respective second exhaust-gas turbocharger 14 a, 14 b of the respective cylinder row 11 a, 11 b. A curve profile 52 visualizes the state of the air recirculation valves 35 a, 35 b that are assigned to the second charge-air lines 24 a, 24 b. A curve profile 53 visualizes the state of the overrun air recirculation valves 34 a, 34 b that are assigned to the first charge-air lines 19 a, 19 b. A curve profile 54 illustrates the profile with respect to time of an ignition angle of the internal combustion engine 10. A curve profile 57 illustrates a controller demand for a charge pressure upstream of the throttle flap 30. A curve profile 56 illustrates a controller demand for a torque reserve. A curve profile 55 illustrates the profile with respect to time of the charge pressure that is actually generated.

Before the time t1 in FIG. 4, the cylinder rows 11 a, 11 b of the internal combustion engine 10 are operated in single-charger operation. Thus, the outlet valves 16 a, 16 b of the cylinders 12 a, 12 b of the cylinder rows 11 a, 11 b are operated with maximum lift and the outlet valves 21 a, 21 b of the cylinders 12 a, 12 b of the cylinder rows 11 a, 11 b are operated with minimum lift or with zero lift. As per the curve profile 52, the air recirculation valves 35 a, 35 b are open before the time t1, whereas the overrun air recirculation valves 34 a, 34 b are closed. Likewise, before the time t1, the compressor activation valves 36 a, 36 b are closed. The wastegate valves 31 a, 31 b interact with the first exhaust-gas turbochargers 13 a, 13 b and regulate the required charge pressure before the time t1 as per the curve profile 50. The throttle flap 30 is open. As per the curve profile 54, the ignition angle is set to an ignition angle to ensure optimum efficiency of the engine 10. The outlet valves 21 a, 21 b are operated with minimum lift or alternatively with zero lift. Thus, a minimal exhaust-gas flow rate, or no exhaust gas at all, passes into the region of the second exhaust-gas turbochargers 14 a, 14 b. Rather, the air recirculation valves 35 a, 35 b open so that the charge air is discharged to the surroundings. Then, no counterpressure is generated at the closed compressor activation valves 36 a, 36 b to avoid an increase in temperature of the charge air. A fuel-air mixture is set to the mixture quality required by the present operating strategy, for example to a lambda value of 1.

At the time t1, as per the curve profile 48, the speed of the internal combustion engine 10 overshoots a threshold value G1. Here, a controller identifies that the cylinder rows 11 a, 11 b are to be switched from single-charger operation to two-charger operation.

The preparation for the switch starts at the time t1 in FIG. 4 and is completed at the time t3. The switch of the respective cylinder row 11 a, 11 b from single-charger operation to two-charger operation is performed following the time t3.

A controller demands an increase in the charge pressure upstream of the throttle flap 30 starting at the time t1 in the curve profile 57 in preparation for the switch from single-charger operation to two-charger operation of the respective cylinder row 11 a, 11 b in the event of operation of the internal combustion engine 10 above the induction-based full load. A torque reserve also is demanded by a controller at the time t2 in the curve profile 56.

Furthermore, at the time t1 in the curve profile 50, previously open wastegate valves 31 a, 31 b are closed, and closed wastegate valves 32 a, 32 b are kept closed. The ignition angle is adjusted in a retarding direction from the position for optimum efficiency, as per the curve profile 54, to maintain a driver demand torque following the increase in the charge pressure upstream of the throttle flap 30 in the case of a constant driver demand torque. The adjustment of the ignition angle is performed with the aim of maintaining a driver demand torque unchanged, in particular keeping the driver demand torque constant. Thus, a torque reserve can be provided in this way.

During the preparation for the switch between the times t1 and t3, the first outlet valves 16 a, 16 b of the cylinders 12 a, 12 b of the cylinder rows 11 a, 11 b continue to be operated with maximum lift, and the outlet valves 21 a, 21 b of said cylinders continue to be operated with minimum lift or alternatively with zero lift.

Between the times t1 and t3, the air recirculation valves 35 a, 35 b are held open, as per the curve profile 52, and the overrun air recirculation valves 34 a, 34 b are kept closed, as per the curve profile 53. Likewise, during the preparation for the switch from single-charger operation to two-charger operation of the respective cylinder row 11 a, 11 b, the respective compressor activation valve 36 a, 36 b also is kept closed. To ensure the desired increase in charge air upstream of the throttle flap 30, it is possible, if appropriate, for the throttle flap 30 to be partially closed.

During the preparation for the switch, the quality of a fuel-combustion air mixture is adapted to the mixture quality demanded by the operating strategy, for example to a lambda value of 1.

At the time t3, the charge pressure overshoots or reaches a threshold value G2 (see curve profile 55). At the time t3, the preparation for the switch from single-charger operation to two-charger operation of the respective cylinder row 11 a, 11 b is completed. As shown from the curve profile 49, at the time t3, a switch is made to two-charger operation at the respective cylinder row 11 a, 11 b. Starting at the time t3, all of the outlet valves 16 a, 21 a and 16 b, 21 b of the cylinders 12 a, 12 b of the respective cylinder row 11 a, 11 b are operated with maximum lift.

The flow cross section of the air recirculation valves 35 a, 35 b may be relevant to avoid surging of the compressor that is to be activated during the switch to two-charger operation. Surging, or a backward flow of already-compressed charge air, can lead to undesired noises and mechanical loading of the exhaust-gas turbocharger. This can be avoided through corresponding dimensioning of the flow cross section of the air recirculation valves 35 a, 35 b.

Accordingly, those outlet valves 21 a, 21 b of the cylinders 12 a, 12 b of the cylinder rows 11 a, 11 b that were previously operated with minimum lift or alternatively with zero lift are switched to maximum lift at the time t3.

As per the curve profiles 56 and 57, starting at the time t3, the increase in charge pressure demanded by a controller, and the torque reserve demanded by a controller, are continuously withdrawn.

After the switch from single-charger operation to two-charger operation of the respective cylinder row 11 a, 11 b at the time t3, the ignition angle is adjusted in the advancing direction, or in the direction of a position for optimum efficiency, again as per the curve profile 54, and the air recirculation valves 35 a, 35 b remain held open for a defined period of time Δt between the times t3 and t4, as per the curve profile 52. Thus, air recirculation valves are closed continuously or abruptly starting at the time t4 up until the time t5.

The overrun air recirculation valves 35 a, 35 b are held closed even during two-charger operation, as per the curve profile 53, and the compressor activation valves 36 a, 36 b are opened, specifically either actively by way of the control device 39 or, in the case of spring-loaded check valves, passively owing to the increase in charge pressure upstream thereof.

After the actual switch at the outlet valves 21 a, 21 b from minimum lift, or alternatively zero lift, to maximum lift, it is accordingly the case that, firstly, the ignition angle is adjusted back in the direction of optimum efficiency, and subsequently, the air recirculation valves 35 a, 35 b are closed. The delayed closing of the air recirculation valves 35 a, 35 b serves in particular for preventing undesired generation of noise.

The elimination of the torque reserve and the adjustment of the ignition angle back in the direction of optimum efficiency may be performed instantaneously, which would give rise to a delayed build-up of speed at the second turbochargers 14 a, 14 b.

What is preferred is a gradual elimination of the torque reserve and adjustment of the ignition angle back in the direction of optimum efficiency, in order thereby to utilize the advantage of the ignition angle on the exhaust-gas enthalpy and on a more rapid build-up of charge pressure at the second exhaust-gas turbochargers 14 a, 14 b.

The mixture quality of the fuel-combustion air mixture is set to the mixture quality demanded by the operating strategy, preferably to a lambda value of 1.

The above preparation and execution of the switch from single-charger operation to two-charger operation of the respective cylinder row 11 a, 11 b are of importance in particular when the switch is performed above the induction-based full load of the internal combustion engine.

The other switches between single-charger operation and two-charger operation of the respective cylinder row 11 a, 11 b, that is to say the switch from single-charger operation to two-charger operation of the respective cylinder row 11 a, 11 b below the induction-based full load of the internal combustion engine, and the switch from two-charger operation to single-charger operation of the respective cylinder row 11 a, 11 b, be it above the induction-based full load or below the induction-based full load, are less demanding. It is sufficient here, during the switch from two-charger operation to single-charger operation, for the second outlet valves 21 a, 21 b of the cylinders 12 a, 12 b to be switched from maximum lift to minimum lift or alternatively to zero lift, and during the switch from single-charger operation to two-charger operation, for the second outlet valves 21 a, 21 b of the cylinders 12 a, 12 b to be switched from minimum lift, or alternatively zero lift, to maximum lift, and for the charge pressure to be regulated by way of the wastegate valves 31 a, 31 b, 32 a, 32 b and/or the throttle flap 30.

The invention also relates to a control device 39 for carrying out the method. The control device 39 is preferably an engine control unit. The control device 39 comprises means for carrying out the method. Said means include hardware means and software means. The hardware means are data interfaces for the exchange of data with the units involved in carrying out the method, a processor for data processing, and a memory for data storage. The software means are program modules of engine control software. 

What is claimed is:
 1. A method for operating an internal combustion engine that has at least one cylinder row with multiple cylinders, the cylinder row having a first exhaust-gas turbocharger and a second exhaust-gas turbocharger, the method comprising providing charge air for the cylinders of the internal combustion engine either exclusively by the first exhaust-gas turbocharger of the or of each cylinder row of the internal combustion engine or by both the first exhaust-gas turbocharger of the cylinder row of the internal combustion engine and the second exhaust-gas turbocharger of the cylinder row of the internal combustion engine in a manner dependent on an operating mode demanded by a driver and/or by a controller for the internal combustion engine.
 2. The method of claim 1, further comprising providing charge air for the cylinders of the internal combustion engine either exclusively by the first exhaust-gas turbocharger of the cylinder row of the internal combustion engine or by both the first exhaust-gas turbocharger of the cylinder row of the internal combustion engine and by the second exhaust-gas turbocharger of the cylinder row of the internal combustion engine in a manner that further is dependent on torque provided by the internal combustion engine and/or in a manner dependent on speed of the internal combustion engine.
 3. The method of claim 2, further comprising: providing charge air for the cylinders of the internal combustion engine exclusively by the first exhaust-gas turbocharger of the cylinder row of the internal combustion engine when: an economy operating mode is demanded; the torque provided by the internal combustion engine is above a torque threshold; and speed of the internal combustion engine are below an engine speed threshold; providing charge air for the cylinders of the internal combustion engine by both the first exhaust-gas turbocharger of the cylinder row and the second exhaust-gas turbocharger of the cylinder row when the speed of the internal combustion engine is above the engine speed threshold; and providing charge air for the cylinders of the internal combustion engine by both the first exhaust-gas turbocharger of the cylinder row and the second exhaust-gas turbocharger of the cylinder row of the internal combustion engine when in the economy operating mode and when the torque provided by the internal combustion engine is below the torque threshold, regardless of the speed of the internal combustion engine.
 4. The method of claim 1, further comprising providing charge air for the cylinders of the internal combustion engine either exclusively by the first exhaust-gas turbocharger of the cylinder row of the internal combustion engine or by both the first exhaust-gas turbocharger of the cylinder row of the internal combustion engine and by the second exhaust-gas turbocharger of the or of each cylinder row of the internal combustion engine in a manner dependent on the operating mode demanded by a driver and/or by a controller for the internal combustion engine, and further dependent on power of the internal combustion engine.
 5. The method of claim 4, further comprising providing charge air for the cylinders of the internal combustion engine by both the first exhaust-gas turbocharger of the cylinder row and the second exhaust-gas turbocharger of the cylinder row of the internal combustion engine when: a sport operating mode is demanded and a power of the internal combustion engine is above a power threshold is demanded by the driver; and providing charge air for the cylinders of the internal combustion engine exclusively by the first exhaust-gas turbocharger of the cylinder row of the internal combustion engine when: the sport operating mode is demanded and the power of the internal combustion engine is below the power threshold is demanded by the driver.
 6. The method of claim 5, wherein the economy operating mode for the internal combustion engine and/or the sport operating mode for the internal combustion engine is demanded by a driver by actuation of a switch or a button.
 7. The method of claim 1, further comprising providing charge air for the cylinders of the internal combustion engine exclusively by the first exhaust-gas turbocharger of the cylinder row of the internal combustion engine when a catalytic converter heating operating mode is demanded.
 8. The method of claim 7, wherein the catalytic converter heating operating mode for the internal combustion engine is demanded by a controller.
 9. The method of claim 1, wherein the cylinders of the respective cylinder row of the internal combustion engine are coupled by first outlet valves and a first exhaust-gas duct to a turbine of the first exhaust-gas turbocharger of the respective cylinder row and by second outlet valves and a second exhaust-gas duct to a turbine of the second exhaust-gas turbocharger of the respective cylinder row, a compressor of the respective first exhaust-gas turbocharger delivering charge air in the direction of the cylinders via a first charge-air line and a compressor of the respective second exhaust-gas turbocharger delivering charge air in the direction of the cylinders via a second charge-air line, the first charge-air line being assigned an overrun air recirculation valve, and the second charge-air line being assigned an air recirculation valve and a compressor activation valve, the method further comprising: providing charge air for the cylinders of the internal combustion engine exclusively by the first exhaust-gas turbocharger of the cylinder row of the internal combustion engine in a steady-state operating state while operating the first outlet valves with a large valve lift and operating the second outlet valves with a small valve lift, with the overrun air recirculation valve assigned to the respective first charge-air line being closed, the air recirculation valve assigned to the respective second charge-air line being opened, and the compressor activation valve assigned to the respective second charge-air line being closed; and providing charge air for the cylinders of the internal combustion engine by both the first exhaust-gas turbocharger of the cylinder row and the second exhaust-gas turbocharger of the cylinder row of the internal combustion engine, in a steady-state operating state while operating the first and the second outlet valves with the large valve lift, with the overrun air recirculation valve assigned to the respective first charge-air line being closed, the air recirculation valve assigned to the respective second charge-air line being closed, and the compressor activation valve assigned to the respective second charge-air line being open.
 10. A control device of an internal combustion engine, comprising means for carrying out the method of claim
 1. 